Circuit protector

ABSTRACT

A circuit protector comprises a permanent magnet secured centrally within a casing and holding as attracted to both N- and S- poles on one surface thereof a movable body of magnetic and electrically conductive material, which has its one end mounted to a terminal on the casing by means of a U-shaped spring, which also acts to bias the movable body away from the magnet. The other end of the movable body is engaged by a reset button slidably mounted on the casing. An opening and closing contact is interposed in the current path between the free end of the movable body and another terminal mounted on the casing. Upon current flow in excess of a given value across the terminals, the movable body moves away from the magnet and interrupts the circuit.

0 United States Patent [1 1 [111 3,743,982

Kasahara 1 ,iuiy 3, W73

[ 1 CIRCUIT PROTECTOR Primary Examiner- Roy N. Envall, Jr. [75} Inventor: Yasuo KasaharaTokWJaPan Attorney-William D. Hall, Elliott I. Pollock et a1.

[73] Assignee: Kabushiki-Kaisha Nakatani,

Tokyo, Japan, a part interest [57] ABSTRACT [22] Fil d; Jan, 13, 1972 A circuit protector comprises a permanent magnet se- 21 Appl. No.: 217,602

[30] Foreign Application Priority Data n- 1971 Japan 46/1783 [56] References Cited UNITED STATES PATENTS 12/1965 Fasola, Jr. 200/67 F 9/1969 Linton 335/208 cured centrally within a casing and holding as attracted to both N- and S- poles on one surface thereof a movable body of magnetic and electrically conductive material, which has its one end mounted to a terminal on the casing by means of a U-shaped spring, which also acts to bias the movable body away from the magnet. The other end of the movable body is engaged by a reset button slidably mounted on the casing. An opening and closing contact is interposed in the current path between the free end of the movable body and another terminal mounted on the casing. Upon current flow in excess of a given value across the terminals, the movable body moves away from the magnet and interrupts the circuit.

9 Claims, 4 Drawing Figures /I/I/I/II /r/, 2 l A Patented Jill 3,1913

2 Shoots-Sheet l Patented July 3, 1973 3,743,982

2 Shoots-Shoot 2 CIRCUIT PROTECTOR BACKGROUND OF THE INVENTION The invention relates to a circuit protector which provides circuit interruption upon current flow therethrough in excess of a given value.

As disclosed in 11.8. Pat. Nos. 3,453,566 and 3,605,047 issued July 1, 1969 and Sept. 14, 1971, respectively, the inventor has previously proposed circuit protectors of the type including a body of magnetic and electrically conductive material carrying a circuit current and arranged so as normally to be held attracted by a permanent magnet, but which is operable to effect relative movement between the magnet and the body in response to the current exceeding a given value to thereby interrupt the current path. Such circuit protectors provide delayed interruption in response to an overload current of magnitude relatively slightly exceeding the rated current, and also provide instantaneous interruption in response to an overcurrent such as shortcircuit current. The circuit protectors are characterized by a short time delay in its delayed interruption operation, and by a rapid interruption in its instan taneous interruption operation. The circuit protectors can be reset subsequent to the circuit interruption. However, the reset operation has been achieved in the earlier constructions by moving the magnet, from the exterior of the casing, toward the body which then is spaced apart from the magnet, whereupon the magnet is returned to its original position together with the body. Because the magnet had to be held in a movable manner, the mechanical construction therefor has become complicated. For example, while a permanent magnet includes a pole piece attached to its body, such a composite, structure cannot be secured to another member as by screw. Of all the components of the circuit protector, the permanent magnet is a relatively large one, and in addition, in use, it must be held in a stable manner so as to prevent external mechanical vibrations and shocks from readily causing its movement. In these respects, the holding structure for the magnet was disadvantageously troublesome and required a relatively large space for its installation.

Therefore, it is an object of the invention to provide a circuit protector which is compact and simple in construction and which is less susceptible to external influences such as mechanical vibrations.

SUMMARY OF THE INVENTION In accordance with the invention, the permanent magnet is fixedly secured substantially centrally within a casing. Reset operation is performed by the movement of the body of magnetic and electrically conductive material, rather than by movement of the magnet. The casing may be moulded from synthetic resin, for example, and formed with a recess for mounting the magnet, the recess being located centrally within the casing and being capable of holding the magnet by merely fitting it therein. The body is of small size and can be held for pivotal movement by simple means e.g., by a biasing spring. No additional space is required for the reset mechanism, since the body is inherently designed for movement to provide circuit interruption upon occurrence of an overcurrent.

BRIEF DESCRIPTION OF THE DRAWINGS Above and other objects, arrangements and effects of the invention will be apparent from the following description with reference to the drawings, in which:

FIG.1 is a front view, partly in longitudinal section, of an embodiment of the circuit protector according to the invention,

FIG.2 is a cross section taken along the line AA shown in FIG.1,

FIG.3 is a perspective view of the circuit protector shown in FIG.1, and

FIG.4 is a schematic circuit diagram showing an exemplary application of the circuit protector of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the circuit protector includes a casing l which is moulded from synthetic resin. The casing 1 comprises a bottom plate la, top plate 1b, left-hand side plate 1c, right-hand side plate 1d, front plate 1e and rear plate If. The top plate lb, both side plates 1c and 1d and rear plate 1f are moulded to provide an integral structure, to the periphery of which is fitted the bottom plate 1a. The front plate 1e is attached to the structure by means of screws.

Adjacent the right-hand side plate 1d, the bottom plate 1a is formed with an aperture for receiving a first terminal member 2 which is secured in place by locking means (not shown), the terminal member 2 extending both inwardly and externally of the casing 1. Second and third terminal members 3 and 4 are fixedly mounted in the bottom plate la at positions intermediate both side plates and adjacent the left-hand side plate 1c, respectively, A plate-like body 5 of magnetic and electrically conductive material 5 extends centrally within the casing 1 between the bottom and top plates 1a and lb. The body 5 is formed of a magnetic material which exhibits a relatively large variation of its magnetic permeability with temperature change and which also exhibits an electrical conductivity. For example, it may comprise so-called magnetic compensating steel which is sometimes used in the pole piece of a permanent magnet.

One end of the body 5 is located adjacent to the second terminal member 3 on the side thereof nearer the third terminal member 4, and the parts 3 and 5 are connected together by a U-shaped leaf spring 6 so that the body 5 is pivotable about the leaf spring 6. The first terminal member 2 extends parallel to the right-hand side plate 1d and then is bent toward the body 5 at a position intermediate the bottom and top plates la and lb. A U-shaped leaf spring 7 has its one end secured substantially at right angles to the bent end of the terminal member Z'and has its other end located closely adjacent to the free end of body 5 adjacent to the top plate 1b. Opening and closing contacts 8 and 9 are mounted in this region on the body 5 and the leaf spring 7, respectively, and are normally in contact with one another.

lntermediate the first terminal member 2 and the body 5, a holder 10 is formed integrally with and projects from the inner surface of the rear plate lf, and a recess 11 is formed in its surface opposite to the body 5 in which recess a permanent magnet 12 is fitted and secured in place, the magnet holding the body 5 attracted thereto. Both the N- and S- poles of the magnet 12 confront the body 5, and said poles are spaced apart crosswise or lengthwise of the body 5. When the body 5 is held attracted by the magnet 12, the resilience of the U-shaped leaf spring 6 biases the body 5 in a direction away from the magnet 12 with a force which is less in magnitude than the force of the magnetic attraction between body 5 and magnet 12. The third terminal member 4 extends to a position adjacent the body 5, and an extension 4a of the terminal member 4 extends along a reinforcing member 13 that extends from the rear plate If on the opposite side of the body 5. At a position opposite to the extension 40, the body 5 carries a contact 14.

The top plate lb is centrally formed with an outward protrusion 15, through which a reset button 16 extends for slidable, bidirectional movement in a direction generally parallel to the bottom plate 1a. In a portion of the button 16 disposed within the casing 1, the reset button is formed with a small aperture 17 in which the free end of the body 5 is inserted for engagement, whereby any motion of the free end of body 5 causes a corresponding motion of button 16, and vice versa. On the top surface of the protrusion are marked designations ON and OFF (see FIG. 3) corresponding to either direction to which the button projects from said protrusion, the set position or ON position being shown in solid line in FIG. 1.

The bottom plate In is formed with a recess 18 in which is received the U-shaped leaf spring 6 interconnecting the second terminal member 3 and the body 5. The holder 10 is formed with a threaded aperture 19 for engagement with a screw that secures the front plate 1e in place. The front plate 1e may be formed with an integral boss boss (not shown) which can be located within a notch 21 formed in the reinforcing member 13 for the purpose of correctly positioning the front plate.

The circuit protector described above may be connected as shown schematically in FIG. 4. The first and second terminal members 2 and 3 are connected through a power source to a circuit 23 to be protected. An alarm unit 24 is connected between the third terminal member 4 and the junction of the circuit 23 and the power source 25. With this connection, when an overload current or short circuit current passes through body 5 via the first and second terminal members, the magnetic attraction between body 5 and magnet 12 is diminished by virtue of a reduction in the magnetic permeability of the body 5 caused by Joule heat, and by virtue of the interaction between the flux from the magnet 12 and that produced by the current flow through the body 5, generally in the manner described in US. Pat. No. 3,453,566. As a result, when such overload current or short circuit current occurs, the body 5, under the influence of the bias provided by springs 6 and 7, moves away from the magnet 12 to the position shown in phantom lines in FIG. 1, whereby the contacts 8 and 9 are disengaged from each other to interrupt the circuit, thus protecting the circuit 23. Simultaneously the contact 14 carried by the body 5 moves into contact with the extension 4a of the third terminal member 4, whereby the power source 25 is connected with the alarm unit 24 to operate it, thus announcing that the circuit 23 is disconnected. The pivotal motion of causes body 5, the reset button 16 to be moved to its OFF position, indicating that the current path between the first and second terminal members is disconnected.

If now the reset button 16 is operated in the reverse direction, i.e. to the ON side, the body 5 resumes its original position by pivotal motion, is again held attracted by the magnet 12, and the circuit protector is restored to its set position. An alarm fuse is known in the field of wire communication which provides a fusing in response to current flow in excess of a given value and controls an alarm driving contact. When used as illustrated in FIG. 4, the circuit protector of the invention can provide a protective function similar to such alarm fuse, with the advantage that its operation is not limited to a single use, but can be repeated by operation of the reset button 16. The provision of the stationary magnet, cooperating with the body 5 which is directly moved upon resetting, simplifies the arrangement for holding the magnet 12, that is, it need merely be fitted into the recess 11 formed in the holder 10 which is integral with the casing. The space within the casing 1 is efficiently utilized as a whole by arranging the magnet 12 and the third terminal member 4 on opposite sides of the body 5, and by disposing the first terminal member 2 to surround the magnet 12 and the holder 10 therefor, with the first terminal member 2 being partly bent. In this manner, the circuit protector can be constructed in a size as small as the prior art alarm fuse.

It is obvious that the above embodiment can be modified and changed in various ways by one skilled in the art without departing from the scope of the invention. Therefore, it is intended that the appended claims cover all such modifications and changes as fall within the scope of the invention.

What is claimed is:

1. A circuit protector comprising a casing of an insulating material having a top plate and a separable bottom plate, first and second spaced terminal members fixedly mounted on said bottom plate and extending internally and externally of said casing, a permanent magnet secured at a fixed position substantially centrally within the casing intermediate said first and second terminal members, a body of magnetic and electrically conductive material normally held attracted by both N- and S- poles of the permanent magnet, said body comprising a material having a magnetic permeability which is subject to a large variation with temperature changes resulting from excessive current flow therethrough, the body having its opposite ends electrically connected to the first and second terminal members respectively, whereby excessive current flowing between said first and second terminals via said body is operative to vary the magnetic attraction between said magnet and body, means for holding one end of the body for pivotable movement with respect to the permanent magnet, the inner end of said first terminal member extending past the side of the permanent magnet facing the top plate of the casing to a position closely adjacent the free end of the body, a pair of opening and closing contacts placed between the free end of the body and the first terminal member in series therewith, and means for biasing the body in a direction away from the permanent magnet.

2. A circuit protector according to claim 1, further including a third terminal member fixedly mounted on the casing and extending internally and externally thereof, and second opening and closing contacts placed between the third and second terminal members respectively and adapted to be controlled by pivotal motion of the body.

3. A circuit protector according to claim 1, further including a hollow protrusion extending outwardly from the casing, a reset button extending through the side walls of the protrusion for bidirectional movement in the direction of motion of the free end of said pivotally mounted body, and means within the casing for en gaging the reset button with the free end of the body.

4. A circuit protector according to claim 1, further including a conductive leaf spring mounted on the first terminal member at a position adjacent the free end of the body, said pair of contacts being mounted respectively on the leaf spring and body, said leaf spring urging said contacts into engagement with each other.

5. A circuit protector according to claim 1, in which the biasing means comprises a U-shaped leaf spring having its one limb secured to one end of the body and its other limb secured to the second terminal member, said biasing means supporting the body for pivotal motion.

6. A circuit protector according to claim 2, in which the third terminal member is mounted in the bottom plate on the opposite side of the second terminal member from the permanent magnet.

7. A circuit protector comprising a casing of insulating material, first and second laterally spaced terminal members fixedly mounted in the bottom plate of the casing and extending internally and externally thereof, a permanent magnet secured substantially centrally within the casing intermediate the first and second terminal members, a plate-shaped body of magnetic and electrically conductive material, the body being normally held attracted to both theN- and S- pole of the permanent magnet and having a magnetic permeability which is subject to a large variation with tempeiature change, a U-shaped conductive leaf spring having its limbs secured to the second terminal member and to one end of said body respectively, said leaf spring being operative to bias the body in a direction away from the permanent magnet, a second conductive leaf spring secured to the first terminal member adjacent the other end of the body, a first pair of opening and closing contacts interposed between the second leaf spring and the body, the second leaf spring being effective to urge the contacts into abutment and to bias the body in a direction away from the permanent magnet, a hollow protrusion formed in the top plate of the casing and extending externally thereof, a rod-shaped reset button slidably extending through lateral sidewalls of the hollow protrusion, and means for holding a portion of the body in engagement with the reset button, the sum of the biasing force of the U-shaped and second leaf springs being greater than the force of attraction acting between the body and the magnet when a current in excess of a given value flows across the first and second terminal members, whereby the body moves away from the magnet to open the circuit between the first pair of contacts upon occurrence of said excess current flow.

8. A circuit protector according to claim 7, further including a third terminal member secured to the bottom plate of the casing on the opposite side from the first terminal member with respect to the second terminal member, and a second pair of opening and closing contacts interposed between the third terminal member and the body and adapted to close when the body moves away from the magnet.

9. A circuit protector according to claim 7, further including a holder formed integrally with the casing and extending inwardly therefrom, said holder including a recess formed therein for reception of the permanent magnet. 

1. A circuit protector comprising a casing of an insulating material having a top plate and a separable bottom plate, first and second spaced terminal members fixedly mounted on said bottom plate and extending internally and externally of said casing, a permanent magnet secured at a fixed position substantially centrally within the casing intermediate said first and second terminal members, a body of magnetic and electrically conductive material normally held attracted by both N- and S- poles of the permanent magnet, said body comprising a material having a magnetic permeability which is subject to a large variation with temperature changes resulting from excessive current flow therethrough, the body having its opposite ends electrically connected to the first and second terminal members respectively, whereby excessive current flowing between said first and second terminals via said body is operative to vary the magnetic attraction between said magnet and body, means for holding one end of the body for pivotable movement with respect to the permanent magnet, the inner end of said first terminal member extending past the side of the permanent magnet facing the top plate of the casing to a position closely adjacent the free end of the body, a pair of opening and closing contacts placed between the free end of the body and the first terminal member in series therewith, and means for biasing the body in a direction away from the permanent magnet.
 2. A circuit protector according to claim 1, further including a third terminal member fixedly mounted on the casing and extending internally and externally thereof, and second opening and closing contacts placed between the third and second terminal members respectively and adapted to be controlled by pivotal motion of the body.
 3. A circuit protector according to claim 1, further including a hollow protrusion extending outwardly from the casing, a reset button extending through the side walls of the protrusion for bidirectional movement in the direction of motion of the free end of said pivotally mounted body, and means within the casing for engaging the reset button with the free end of the body.
 4. A circuit protector according to claim 1, further including a conductive leaf spring mounted on the first terminal member at a position adjacent the free end of the body, said pair of contacts being mounted respectively on the leaf spring and body, said leaf spring urging said contacts into engagement with each other.
 5. A circuit protector according to claim 1, in which the biasing means comprises a U-shaped leaf spring having its one limb secured to one end of the body and its other limb secured to the second terminal member, said biasing means supporting the body for pivotal motion.
 6. A circuit protector according to claim 2, in which the third terminal member is mounted in the bottom plate on the opposite side of the second termInal member from the permanent magnet.
 7. A circuit protector comprising a casing of insulating material, first and second laterally spaced terminal members fixedly mounted in the bottom plate of the casing and extending internally and externally thereof, a permanent magnet secured substantially centrally within the casing intermediate the first and second terminal members, a plate-shaped body of magnetic and electrically conductive material, the body being normally held attracted to both the N- and S-pole of the permanent magnet and having a magnetic permeability which is subject to a large variation with temperature change, a U-shaped conductive leaf spring having its limbs secured to the second terminal member and to one end of said body respectively, said leaf spring being operative to bias the body in a direction away from the permanent magnet, a second conductive leaf spring secured to the first terminal member adjacent the other end of the body, a first pair of opening and closing contacts interposed between the second leaf spring and the body, the second leaf spring being effective to urge the contacts into abutment and to bias the body in a direction away from the permanent magnet, a hollow protrusion formed in the top plate of the casing and extending externally thereof, a rod-shaped reset button slidably extending through lateral sidewalls of the hollow protrusion, and means for holding a portion of the body in engagement with the reset button, the sum of the biasing force of the U-shaped and second leaf springs being greater than the force of attraction acting between the body and the magnet when a current in excess of a given value flows across the first and second terminal members, whereby the body moves away from the magnet to open the circuit between the first pair of contacts upon occurrence of said excess current flow.
 8. A circuit protector according to claim 7, further including a third terminal member secured to the bottom plate of the casing on the opposite side from the first terminal member with respect to the second terminal member, and a second pair of opening and closing contacts interposed between the third terminal member and the body and adapted to close when the body moves away from the magnet.
 9. A circuit protector according to claim 7, further including a holder formed integrally with the casing and extending inwardly therefrom, said holder including a recess formed therein for reception of the permanent magnet. 